The present invention relates to a speed control system for automotive vehicles, and more particularly to an improvement of a speed control system for an automotive vehicle of the type in which the opening angle of the engine throttle is controlled in accordance with the actual speed of the vehicle and the rate of change of the actual speed in relation to a desired command speed.
In such a conventional speed control system as described above, a set switch is closed to produce a set signal when the actual speed of the vehicle reaches a desired value. In response to the set signal, the desired value of the vehicle speed is calculated and memorized, and subsequently a value of the actual speed is repetitively calculated in relation to the memorized value to detect a difference between the desired command speed and the actual speed of the vehicle. Thus, the opening angle of the engine throttle is controlled in accordance with the detected speed difference. This means that the control of the engine throttle may not be conducted at the initial stage to cause undesired change of the actual speed immediately after closing the set switch.